1. Field of the Invention
The present invention relates to a method and an apparatus for processing an audio signal that encode or decode an audio signal.
2. Discussion of the Related Art
In general, auditory masking is explained by psychoacoustic theory. The masking effect uses properties of the psychoacoustic theory in that low volume signals adjacent to high volume signals are overwhelmed by the high volume signals, thereby preventing a listener from hearing the low volume signals. During quantization of an audio signal, a quantization error occurs. Such quantization error may be appropriately allocated using a masking threshold, with the result that quantization noise may not be heard.
However, bits are insufficient for a low bit rate codec, with the result that it is not possible to completely mask such quantization noise. In this case, perceived distortion cannot be avoided, and therefore, it is necessary to allocate bits so as to minimize the perceived distortion.
According to the properties of the human auditory system, on the other hand, a speech signal is more sensitive to quantization noise of a frequency band having relatively low energy than to quantization noise of a frequency band having relatively high energy.
In particular, a psychoacoustic model based on a signal excitation pattern is applied to a signal containing a mixture of speech and music, and therefore, quantization noise is allocated irrespective of the human auditory property. As a result, it is not possible to effectively allocate a quantization error, thereby increasing perceived distortion.